I               L             S






In the Airplane

either of the 2 Instruments:







works​ the same way as when  used with a VOR





shows your horizontal spot in relation to your selected course


“No reverse sensing” **

Ground Station

consists of 2 antennas:

If you remain properly on glide path all the way down to DH (Decision Height), you should be able to land within the Touchdown zone.


For Part 135 and 121 operations,

this is also mandatory.

If this can not be assured due to any reason, the pilot is required to make a 'missed approach' or go around.



positioned ~1000ft

beyond departure end of the RWY

and ~250ft offset from RWY centerline

“responsible for horizontal guidance

250-750 ft

down from the approach end, and 400-600 ft
offset of either

side of Centerline


“responsible for vertical guidance”

- after the Final Approach Course is selected, the operation of the CDI-needle is the same as with the VOR,


!4 times more sensitive!



A full scale deflection is

2.5° off of the extended centerline on either side

(full deflection VOR = 10° off)

**No reverse sensing because the compass card works like a Heading Indicator <> Current heading is ALWAYS on top-half of the instrument. Reverse Sensing would occur if flown heading would be on bottom-half of VOR-Instrument.

The full ILS-System provides you three informations...
1. Guidance Information
(GlideSlope & Localizer)
2. Visual Information
(Approach Lights, T/D & Centerline Lights, RWY Lights)
3. Range Information
(Marker Beacons & DME)
Guidance Information comes from two Ground-based-Components: 
The Glideslope
  • The ILS Glide Path extends horizontally at ~ 3 degrees above AGL to a distance of 4-7 miles (10 NM) parallel to the RWY CTL the Glide Slope may extend at a lower angle, about 2.5 degrees or at steeper angle ~ 3.5 to 4 degrees.


  • If circling around the airport, or if further out than 10 NM, GS indications should be disregarded and not followed.


  • it follows the same principle as the LOC (150 Hz upper part/90Hz lower part)


  • 150 Hz section = 0,7 degress / 90 Hz section = 0,7 degress => 1,4 degress

Useful Formulas

  • To figure out your rate of descent (ROD), you can use the folllowing formular: ground speed (GS) x 5

    EX.: APPR SPEED = 100kts IAS → 100 x 5 = 500fpm (~ 500 feet per minute descent to maintain the GS)


  • To figure out the ALT along your GS → distance in miles from T/D x 300

    EX.: if 2 nm out → 2 x 300 = 600 ft (A/C should be ~ 600ft above TDZE @ 2nm from threshold)

The Localizer

Localizer antenna is positioned ~1000ft beyond the DER (dept. end of RWY) and 250ft offset

from the center of the RWY sending out radio signals.

LOC FRQ Range → 108.10 – 111.95 MHz (all 'ODD' tenths = .30-.50.-.70...)

The Localizer
  • 'off course' indications are limited to 35° either side and should otherwise be disregarded

  • Signals reach out to 18nm from it's position and up to 4,500ft

  • course width is between 3 – 5 deg. (usually ~ 2.5 deg. either side)

  • if the 150Hz signal is stronger, the CDI (needle) will move to the LEFT – and vice versa

  • a centered needle means that both signals are received equal


LOC course
1000ft above 
Highest obstacle
Up to 
4.500ft above
Antenna elev.